In paper manufacturing, printing, or similar applications involving a traveling web, a plurality of rolls are typically utilized for controlling the traveling path of the web.
In order to be able to provide a web product having an even quality across its width, it is typically desirable to determine a web tension profile of the web across its width when the web is in contact with the peripheral surface of a rotating roll. By determining the web tension profile of the web and by evaluating the web tension profile, the tension applied by the web to the roll may be controlled so as to obtain an even tension across the width of the web when in contact with the roll. As a result, a higher quality web may be provided.
In order to be able to measure the web tension profile of the web, sensors may be arranged on the roll for sensing the forces applied by the web on the peripheral surface of the roll. The sensors provide signals which may be evaluated for determining the web tension profile of the web. However, rolls having sensors on the peripheral surface suffer from several disadvantages, such as the sensors protruding from the surface, which necessitates coating of the roll to provide a smooth roll surface.
Sensors may also be implanted in the surface of the roll, as described in US 2004/0030439. US 2004/0030439 discloses a system for detecting the normal force exerted by a web material around the circumferential surface of a cylinder. Multiple sensors may be implanted in the cylinder surface. The cylinder surface may be machined to contain a recess, a cavity or a slot that fits the sensor. The sensor may be disposed in the recess such that the sensor's force-sensitive surface is flush with the cylinder surface.
However, there are drawbacks with the teachings of US 2004/0030439. For instance, the measured web tension profile may be contaminated by various inherent properties of the cylinder. In particular, the system of US 2004/0030439, which is for printing applications, would not be suitable for wide-body cylinder rolls used e.g. in the paper manufacturing industry.